Polymer stabilization



United States Patent 3,379,682 POLYMER STABILIZATION John H. Prichard,Millingtou, N.J., assignor to Celanese Corporation, New York, N.Y., acorporation of Delaware No Drawing. Continuation of application Ser. No.

287,764, June 14, 1963. This application Feb. 15,

1967, Ser. No. 616,198

Claims. (Cl. 260--45.85)

ABSTRACT OF THE DISCLOSURE The present invention relates to oxymethylenepolymers which have been improved as to light stability by incorporationinto said polymers a stabilizing amount of at least one hydroxyphenylester of benzoic acid such as resorcinol monobenzoate.

The present application is a continuation of application Ser. No.287,764, filed June 14, 1963, now abandoned, which is acontinuation-in-part of application Ser. No.

3,257, filed Ian. 19, 1960, now abandoned, both applica-- tions beingassigned to the same assignee as the present invention.

Background of the invention This invention relates to oxymethylenepolymers and particularly to a method for improving the light stabilityof polymers.

Oxymethylene polymers, having recurring CH O- units have been known formany years. They may be prepared by polymerizing a source ofoxymethylene units such as anhydrous formaldehyde or trioxane, a cyclictrimer of formaldehyde.

High molecular Weight solid polyoxymethylenes have been prepared bypolymerizing trioxane in the presence of certain cationic catalysts andmay also be prepared in high yields and at rapid reaction rates by theuse of catalysts comprising boron fluoride coordination complexes withorganic compounds, as described in Patent No. 2,989,506 of Donald E.Hudgin and Frank M. Berardinelli. Boron fluoride gas is also a rapid andeffective catalyst, as disclosed in Patent No. 2,989,507 of Hudgin andBerardinelli. Other catalysts are disclosed in the article by Kern etal. in Angewandte Chemie 73(6) pages 176- 186 (Mar. 21, 1961).

Oxymethylene polymers of improved thermal stability may be prepared byintroducing into the polymer chains, or attaching to the ends of thepolymer chains, structures which are resistant to thermal detachment.The polymers may incorporate interspersed oxyalkylene units withadjacent carbon atoms, preferably oxyethylene units, as disclosed inPatent No. 3,027,352 of Walling, Brown and Bartz. Copolymers of thistype may be described as having at least one chain containingoxymethylene (OCH units (usually at least 85 mol percent) interspersedwith (-O-R) units wherein R is a divalent radical containing at leasttwo carbon atoms directly linked to each other and positioned in thechain between the two valences, with any substituent in the R radicalbeing inert.

Specific interspersed monomeric units which may be incorporated arethose derived from lactones, carbonates, cyclic acid anhydrides orethylenically unsaturated compounds, such as styrene, divinyl ether,vinyl acetate, vinyl methyl ketone or acrolein as disclosed in thearticle by Kern et al. in Angewandte Chemie 73(6) pages 177-186 (Mar.21, 1961). The polymers may be end-capped by acylation or etherificationafter polymerization or during polymerization by the use of selectedchain transfer agents. r

ice

As used in the specification and claims, the term oxymethylene polymersdenotes homopolymers and copolymers (including terpolymers, etc.) havingat least percent recurring oxymethylene (--CH O) units, and furtherincludes substituted homopolymers and copolymers wherein thesubstituents are inert i.e. do not participate in undesirable sidereactions.

Oxymethylene polymers prepared by some methods are quite stable againstthermal degradation and from which molded articles of excellent physicalcharacteristics may be produced. However, where the molded articles areexposed to sunlight for extended periods they have a tendency to undergoembrittlement and surface encrustation.

Summary of the invention In accordance with the present invention thelight stability of oxymethylene polymers is enhanced by the incorportiontherein of at least one hydroxyphenyl ester of benzoic acid having theformula:

wherein R is selected from the group consisting of hydrogen and hydroxyradicals, and

R is selected from the group consisting of hydrogen, halogen, and alkylshaving from 1 to 4 carbon atoms.

Description of the preferred embodiment The light stabilizing compoundsinclude benzoic acid esters, halo benzoic acid esters and alkyl benzoicacid esters of such polyhydroxy phenols, as for example,

catechol OH 3 I: 4 5 :1 OH; Z-hydroxy phenol] resorcinol HO 0 H;3-hydroxy phenol hyd roquinone [HOOE 4hydroxy phenol] pyrogallol [HO 0 HOH; 2,3-dihydroxy phenol] 3 2\ [H041 5 6 1 OH; 3,4-d1hydroxy phenol]phloroglucinol H OH; 8,4-dihydroxy phenol Specifically included are thehydroxyarylbenzoic acid esters, such as 2'-hydroxy-phenyl benzoate3'-hydroxy phenyl benzoate; 4'-hydroxy phenyl benzoate; 2,3'-dihydroxyphenyl benzoate', 3',4'-dihydroxy phenyl benzoate; 3,5'-dihydroxy phenylbenzoate; 2.-hydroxy- 4'-methyl phenyl benzoate; 2'-hydroxy-5-tertiarybutyl phenyl benzoate; 2'-hydroxy-4'-chlorophenyl benzoate;3-hydroxy-5'-methyl phenyl benzoate; 3'-hydroxy-5-tertiary butyl phenylbenzoate; 3'-hydroxy-5'-chlorophenyl benzoate; 4'-hydroxy phenylbenzoate; 2'-hydroxy-4-tertiary butyl phenyl benzoate;2'-hydroxy-4'-ethylphenyl benzoate; 3-hydroxy-5-propylaphenyl lbenzoate;etc., the hydroxy aryl-halo benzoic acid esters, such as2-hydroxyphenyl-4-chloro benzoate 2'-hydroxy-4'-tertiary butylphenyl-3-chlorobenzoate; 3'- hydroxy-5-tertiary butyl-4-chlorobenzoate;4'-hydroxy-4- chlorobenzoate; 2'-hydroxy-4-chlorobenzoate; 3'-hydroxy-S-chlorobenzoate; 2,3'-dihydroxy-4-bromobenzoate; 3',4'-dihydroxy-flbromobenzoate; 2,4'-dihydroxy-4-chlorobenzoate; etc., thehydroxyaryl alkyl benzoic acid esters, such as 4-hydroxy phenylo-toluate -hydroxy phenyl o-toluate; 2'-hydroxy phenyl-3,5- dimethylbenzoate; 2'-hydroxy-5'-tertiary butyl phenyl p-toluate; 2,3-dihydroxyphenyl-4-tertiary butyl benzoate; 3'-hydroxy phenyl-S-ethyl benzoate;2-hydroxy-4'- chloro phenyl-4-tertiary butyl benzoate; 3-hydroxy-5'-chlorophenyl-p-toluate; 3',5'-dihydroxy-4-tertiary butyl phenylbenzoate; etc.

The aforementioned compounds are preferably admixed with theoxymethylene polymers in amounts from about 0.01 percent to about 5percent, based on the weight of the polymer and most preferably inamounts between about 0.25 percent and about 4 percent by weight.

In accordance with one aspect of this invention, the aforesaid lightstabilizing compound is incorporated into an oxymethylene homopolymer,which may be end-capped as by esterification of a terminal hydroxylgroup during or subsequent to polymerization. The homopolymers may beprepared by the polymerization of any suitable source of oxymethyleneunits, such as anhydrous formaldehyde or trioxane, a cyclic trimer offormaldehyde.

In accordance with a preferred embodiment of this invention, theaforesaid light stabilizing compound is incorporated into a copolymerhaving at least one chain containing oxymethylene (CH O-) units(preferably at least 85 mol percent) interspersed with OR units whereinR is a divalent radical containing at least two carbon atoms directlylinked to each other and positioned in the chain between the twovalences with any substituent in the R radical being inert. Thesecopolymers may be prepared, for example, by copolymerizing trioxane witha cyclic ether having the structure CHr-O AER-(0511911 where n is aninteger from zero to two.

Among the specific cyclic ethers which may be used are ethylene oxide,1,3-dioxolane, 1,3,5-trioxepane, 1,3-dioxane, trimethylene oxide,pentamethylene oxide, 1,2propylene oxide, 1,2-butylene oxide, neopentylformal, pentaerythritol diformal, paraldehyde, tetrahydrofuran, andbutadiene monoxide.

The preferred catalysts used in the preparation of the 4 desiredcopolymers are the boron fluoride coordinate complexes with organiccompounds in which oxygen or sulphur is the donor atom.

The coordinate complex of boron fluoride may, for example, be a complexwith a phenol, an ether, an ester, or a dialkyl sulfide. Boron fluoridedibutyl etherate, the coordinate complex of boron fluoride with dibutylether, is the preferred coordinate complex. The boron fluoride complexwith diethyl ether is also very eifective. Other boron fluoridecomplexes which may be used are the complexes with methyl acetate, withethyl acetate, with phenyl acetate, with dimethyl ether, withmethylphenyl ether and with dimethyl sulfide.

The coordinate complex of boron fluoride should be present in thepolymerization zone in amounts such that its boron fluoride content isbetween about 0.001 and about 1.0 weight percent based on the weight ofthe monomers in the polymerization zone. Preferably, amounts betweenabout 0.003 and about 0.1 weight percent should be used.

The monomers in the reaction zone are preferably anhydrous orsubstantially anhydrous. Small amounts of moisture, such as may bepresent in commercial grade reactants or may be introduced by contactwith atmospheric air will not prevent polymerization, but should beessentially removed for best yields.

One method for preparing the oxymethylene polymers comprises dissolvingthe trioxane, cyclic ether (if any) and catalyst in a common anhydroussolvent, such as cyclohexane, and permitting reaction in a sealedreaction zone. The temperature in the reaction zone may vary from about0' C. to about C. The period of reaction may vary from about 5 minutesto about 72 hours. Pressures from subatmospheric to about 100atmospheres may be used, although atmospheric pressure is preferred.

Upon completion of the polymerization reaction it is desirable toneutralize the activity .of the polymerization catalyst since prolongedcontact with the catalyst degrades the polymer. The polymerizationproduct may be treated with an aliphatic amine, such as tri-nbutylamine,in stoichiometric excess over the amount of free catalyst in thereaction product, and preferably in an organic Wash liquid which is asolvent for unreacted trioxane. Or, if desired, the reaction product maybe washed with water which neutralizes catalyst activity.

A detailed description of the methods of neutralizing catalyst activitymay be found in U.S. Patent 2,989,509 of Donald E. Hudgin and-Frank M.Berardinelli.

In a preferred embodiment of this invention the polymer composition alsocontains a thermal stabilizer, such as a phenolic material.

Among the suitable phenolic materials are aliphatic and alicyclicphenols such as p-octyl phenol, p-phenyl phenol, p-cyclohexyl phenol,and alkylene bisphenols.

A suitable class of alkylene bisphenols includes compounds having from 1to 4 carbon atoms in the alkylene group and having from zero to twoalkyl substituents on each benzene ring, each alkyl substit-uent havingfrom 1 to 4 carbon atoms. The preferred alkylene bisphenols are2,2-methylene bis-(5-methyl-6-tertiary butyl phenol); 2,2'-methylenebis-(4-methyl-6-tertiary butyl phenol); 2,2-methylenebis(4-methyl-6-methyl cyclohexyl phenol); and 4,4-butylidenebis-(6-tertiary butyl-3-methy1 phenol).

Other stabilizers include amine compounds, such as diphenyl amine, andN,N,N',N-tetrakis (Z-hydroxypropy1)-1,2-ethylene diamine.

The thermal stabilizer, when used, is preferably admixed with theoxymethylene polymer in amounts from about 0.01 percent to about 2percent based on the weight of polymer and most preferably in amountsbetween about 0.1 percent and about 1 percent by weight.

The aforementioned light stabilizers, and the thermal stabilizers, ifdesired, may be admixed intimately with the oxymethylene polymer bybeing applied in solution in a suitable solvent to the finely dividedsolid oxymethylene polymer followed by evaporation of the solvent.Diethyl ether, methanol, ethanol and acetone are typical suitablesolvents. I

The admixture may also be made by dry blending the finely dividedoxymethylene polymer and finely divided stabilizers, by milling thestabilizers into the polymer as the latter is worked on a rubber mill orby dissolving the oxymethylene polymers and the stabilizers in a commonsolvent, such as dimethyl formamide.

The compositions of this invention may also include, if desired,plasticizers, fillers and other components which influence the finalproperties of the molded product.

Example I To 150 g. of trioxane heated to 90 C., 0.05 g. BF

etherate was added with stirring, the mixture solidifying almostimmediately and the temperature rising to 100 C. After removal from thevessel and pulverizing, the polymer was washed for /2 and 1 hour periodsrespectively, by refluxing with two portions of distilled water at 95-98 C. After drying 16 hours at 60 C., the resultant 80 g. ofpolyoxymethylene had an intrinsic viscosity of 1.3 in p-chlorophenol at60 C. r

A portion of the above described polymer was slurried in a diethyl ethersolution of diphenylamine and resorcinal monobenzoate, containing enoughdiphenylamine to deposit 2 weight percent thereof on the polymer andenough resorcinol monobenzoate to deposit 4 weight percent on thepolymer. The slurry was dried and the polymer was compression-molded at180 C. and 1500 psi. for 3 minutes to produce a disc having a diameterof 2.2 inches and a thickness of 20 mils. The disc was exposed in a X-1AWeatherometer (artificial weathering apparatus type D described in ASTME-42-57) for an extended period and compared with respect toembrittlement and surface encrustation with other discs made up asdescribed below.

Example H Example I was repeated except that the resorcinol monobenzoatewas omitted from the treating solution.

Example III Example I was repeated except that the treating solutioncontained p-cyclohexyl phenol (enough to deposit 5 weight percent on thepolymer) and resorcinol monobenzoate (enough for 2 weight percent on thepolymer).

Example IV Example I was repeated except that the treating solutioncontained N,N,N',N' tetrakis (2-hydroxypropyl)-l,2 ethylene diamine(enough to deposit 1 weight percent on the polymer), p-octyl phenol(l,1,3,3 tetramethylbutyl phenol, enough for 2 percent on the polymer)and resorcinol monobenzoate (enough for 4 percent on the polymer).

The results of accelerated weathering in the Weatherometer on the discsof the above examples was as follows:

Example N 0. Hours to Produce Surface Embrittlement Encrustatiow 400Moderate. 100 eavy 400 Light. 800 Moderate.

Embrittlement was determined by observing the behaviour of the discswhile cutting them with shears after exposure. Brittle discs developedtransverse cracks while being cut and extremely brittle discs fallapart.

2 Surface encrustation was evidenced by the formation of an opaquewhite, matte surface on the translucent discs.

Example V about parts of methanol having dissolved therein 0.1 part ofcyanoguanidine, 0.5 part of 2,2-methylene bis(4- methyl-6 methylcyclohexyl phenol). The slurry was dried in a vacuum oven and thenmilled in a sigma blade mixer for 15 minutes at 190l94 C. A disc wascompression molded from this polymer at 190 C. and 1600 p.s.i. for 3minutes. When exposed in the Weatherometer as described above, there wasno embrittlement after 800 hours.

By contrast, a disc prepared in an identical manner, except that theresorcinol monobenzoate was omitted, was brittle in less than 100 hours.

It is to be understood that the foregoing detailed description is givenmerely by way of illustration and that many variations may be madetherein without departing from the spirit of my invention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. An oxymethylene polymer composition comprising (1). a moldableoxymethylene polymer, and

(2) at least one hydroxyphenyl ester of benzoic acid having the formula:

OH R

i -oo wherein:

R is selected from the group consisting of hydrogen and hydroxyradicals, and R is selected from the group consisting of hydrogen,halogen, and alkyls having from 1 to 4 carbon atoms, said ester beingpresent in sufficient amount so that said polymer composition exhibits agreater degree of light stability than does said polymer composition inthe absence of said light stabilizing compound.

2. The composition of claim 1, wherein the hydroxyphenyl ester ofbenzoic acid is present in the amount of from about 0.01 to about 5.0%,based on the weight of the polymer.

3. The composition of claim 2, wherein said oxymethylene polymer is acopolymer having at least one chain containing at least mol percentrecurring oxymethylene units interspersed with --O-R units, wherein R isa divalent radical containing at least two carbon atoms directly linkedto each other and positioned in the chain between the two valences withany substituent in the R radical being inert.

4. An oxymethylene polymer composition comprising (1) a moldableoxymethylene polymer, and

(2) from about 0.01 to about 5.0%, based on the weight of the polymer,of an hydroxyphenyl ester of benzoic acid having the formula:

R is selected from the group consisting of hydrogen and hydroxyradicals, and

R is selected from the group consisting of hydrogen, chlorine, bromine,and alkyls having from 1 to 4 carbon atoms.

5. The composition of claim 4, wherein said oxymethylene polymer is acopolymer having at least one chain containing at least 85 mol percentrecurring oxymethylene units interspersed with O--R- units, wherein R-is a divalent radical containing at least two canbon atoms directlylinked to each other and positioned in the chain between the twovalences with any substituent in the R radical being inert.

6. The composition of claim 5, wherein the hydroxyphenyl ester ofbenzoic acid is present in the amount of from about 0.25 to about 4.0%,based on the weight of the polymer.

7. An oxymethylene polymer composition comprising (1) a moldableoxymethylene polymer, (2) from about 0.01 to about 5.0%, based on theweight of the polymer, of an hydroxyphenyl ester of benzoic acid havingthe formula:

wherein:

R is selected from the group consisting of hydrogen and hydroxyradicals, and R is selected from the group consisting of hydrogen,chlorine, bromine, and alkyls having from 1 to 4 carbon atoms, and (3)an alkylene bisphenol having from 1 to 4 carbon atoms in the alkylenegroup and from zero to two alkyl substituents on each benzene ring, eachalkyl substituent having from 1 to 4 carbon atoms, said alkylenebisphenol being present in sufiicient amount so that said polymercomposition exhibits a greater degree of thermal stability than doessaid polymer composition in the absence of said alkylene bisphenol. 8.The composition of claim 7, wherein said oxymethylene polymer is acopolymer having at least one chain containing at least 85 mol percentrecurring oxymethylene units interspersed with --OR units, wherein R isa divalent radical containing at least two carbon atoms directly linkedto each other and positioned in the chain between the two valences withany substitutent in the R r-adic-al being inert, said alkylene bisphenolis present in an amount in the range of from about 0.01 to about 2.0%,based on the weight of the polymer.

9. The composition of claim 8, wherein the hydroxyphenyl ester ofbenzoic acid is 3'-hydroxyphenylbenzoate.

10. The composition of claim 8, wherein the hydroxyphenyl ester ofbenzoic acid is present in an amount of from about 0.25 to about 4.0%,based on the weight of the polymer.

No references cited.

DONALD E. CZAJA, Primary Examiner.

V. P. HOKE, Assistant Examiner.

